A switch mode power supply (SMPS) is used to provide a constant voltage to a load via a low pass filter and using a semiconductor device such as a power transistor (e.g., a MOSFET) as a switch. The semiconductor switches used to implement switch mode power supplies are continuously switched on and off at high frequencies (50 kHz to several MHz), to transfer electrical energy from the input to the output through the passive components.
The efficiency of high input voltage power supplies is limited by the switching losses of the primary MOSFET. Switching losses become the dominant loss for high input voltage applications (automotive, a/c, industrial, etc.).
In addition, high frequency switches produce substantial electromagnetic interference (EMI), which is increasingly the subject of governmental regulation.